1. Field of the Invention
The present invention relates to a thermosettable resin molding compound containing a filler and a process for preparing the same. More particularly, it relates to a prepreg or primix having nontacky surface which comprises a liquid thermosettable resin and a process for preparing the same.
2. Description of Prior Arts
The thermosettable resin molding compounds comprising a reinforcing filler such as reinforcing fibers and a powdery filler such as calcium carbonate are classified to a prepreg and a premix.
The prepreg is prepared by immersing a reinforcing fiber in a thermosettable resin compound. The premix is prepared by blending a reinforcing fiber to a thermosettable resin.
When a liquid thermosettable resin is used as the thermosettable resin for the prepreg or premix, there have been the problems of the volatility of the component of the liquid thermosettable resin and the tackiness of the surface of the molding compound. For example, in the case of a prepreg comprising a styrene crosslinking type unsaturated polyester, the viscosity of the unsaturated polyester has been increased to deteriorate the fluidity and the surface is coated with a nontacky inert film to use the molding compound after peeling off the film in order to overcome the problems. This type of sheet is called as SMC.
On the other hand, the bulk molding compound called as BMC has been known as a premix. BMC is bulk molding compound which is prepared blending styrene crosslinking type unsaturated polyester resin to a large amount of a powdery filler and a reinforcing fiber and increasing the viscosity of the mixture. When it is stored for a long time, BMC is covered with an inert film as the same with the case of SMC. However, it has been required to peel off the film when it is used for the molding and this is disadvantage in the case of a mass production.
In the case of the premix or prepreg prepared by using a solid thermosettable resin (it is in a form of solid at room temperature) such as an unsaturated polyester with a solid crosslinking agent, pellets of the molding compound are used. In the case of the premix prepared by mixing a phenol resin with a filler, pellets of the molding compound are also used. The pellets are easily handled and can be used for a continuous molding process by an injection molding machine advantageously. However, it has not known to use pellets of the molding compound prepared by using a liquid thermosettable resin (at room temperature), because the pellets of the molding compound have large surface area to vaporize a large amount of volatile matters such as styrene and the pellets are adhered each other to form a bulk. The handling is not easy and the molding could not be attained by an injection molding machine without a special feeding device. When pellets are prepared by said method of preparing BMC, it is necessary to cover pellets of the molding compound with the inert film for each pellet and to peel off the inert film before the molding the pellets. This operation is not easy and it is impossible in the practical industrial operation.
It has been considered to be remarkably advantageous that the pellets of the molding compound having nontacky surface can be obtained by using the liquid thermosettable resin such as the styrene crosslinking unsaturated polyester. The pellets of the molding compound can be used for a continuous molding by the conventional injection molding machine with the advantages of the improvement of the processability such as molding velocity; and no requirement of peeling-off of the inert film in the injection molding as well as the compression molding; and the improvement of storage of the molding compound; and a decrease of the cost in comparison with the molding compound prepared by using the solid thermosettable resin. When the molding compound is used for the compression molding, the operation for cutting the mass of the molding compound and weighing desired amount can be eliminated to improve the efficiency for the molding.
The inventor has studied on pellets of molding compound prepared by using a liquid thermosettable resin and has found the molding compound which can be prepared without using an inert film which is peeled off but coating the surface of the molding compound with a nontacky coat for preventing tackiness of the surface and using the molding compound without peeling off the nontacky coat.